JP2009065751A - Method for compensating dc standby voltage of momentary voltage drop compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a matter that the lifetime is short because the discharge time of an electric double layer capacitor used in a momentary voltage drop compensator becomes more than a specified momentary voltage drop operation time owing to the values of the capacitance and the internal resistance after elapsing the lifetime of the compensator. <P>SOLUTION: When the DC voltage and the recharge start voltage of an electric double layer capacitor during stand-by of momentary voltage drop are set, the capacitance and the internal resistance after a predetermined period are determined from a change due to aging of the electric double layer capacitor, and the capacitor voltage during stand-by of momentary voltage drop is determined by substituting the capacitance and the internal resistance for a discharge time calculation formula. The capacitance and the internal resistance are determined every predetermined time and used. Alternatively, an effective power is determined by performing d-q conversion of the detected voltage and load current of a power system, and the effective power thus calculated is substituted for the discharge time calculation formula to determine the capacitor voltage during stand-by of momentary voltage drop thus compensating for the set value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a direct current standby voltage compensation method for an instantaneous voltage drop compensator (hereinafter referred to as an instantaneous voltage drop compensator), and more particularly to a direct current standby voltage compensation method when an electric double layer capacitor is used as an energy storage device.

  A voltage sag compensator using an electric double layer capacitor as an energy storage device is known from Patent Document 1 and the like. FIG. 3 shows a schematic configuration diagram thereof. A high-speed switch 3 is provided between a power supply system 5 and a load. The electric double layer capacitor 1 as a voltage storage device and the AC / DC converter 4 are provided between the high-speed switch 3 and the load. Connected. This system supplies power to the load 2 via the high-speed switch 3 in normal times. When a voltage drop including a power failure occurs in the system voltage, the high-speed switch 3 is disconnected from the system, the DC voltage stored in the electric double layer capacitor 1 is converted into AC by the AC / DC converter 4, and power is supplied to the load 2 without interruption. Supply.

The energy E stored in the electric double layer capacitor can be calculated by E = 1/2 · CV ^{2 from} the DC voltage V of the capacitor.
There are two DC voltage control methods for charging the electric double layer capacitor in normal times: (1) stopping the AC / DC converter, and (2) operating the AC / DC converter in a floating charge operation.

  In the method (1), the AC / DC converter 4 is stopped after charging the capacitor voltage to the rated voltage. When the AC / DC converter 4 is stopped, the capacitor voltage decreases due to the leakage current or the voltage dividing resistor for the electric double layer capacitor. When the capacitor voltage becomes smaller than a certain voltage value, the AC / DC converter 4 is operated to charge the capacitor voltage to the rated voltage again. FIG. 4 shows this state. After charging the capacitor voltage to the rated voltage V1, the AC / DC converter 4 is stopped at time t1. When the time t2 is reached and the voltage drops to the preset voltage V2, the AC / DC converter 4 is charged again to the rated voltage V1. Control in the AC / DC converter 4 at that time is constant voltage control.

In the method (2), the AC / DC converter 4 is always operated as shown in FIG. 5, and the capacitor voltage is controlled to be the rated voltage V1.
That is, in both the methods (1) and (2), the command value for the constant voltage control and the voltage at which the AC / DC converter 4 starts the constant voltage control are fixed.
JP 2006-74903 A

In both the methods (1) and (2), the command value for the constant voltage control and the voltage at which the AC / DC converter 4 starts the constant voltage control are fixed. For this reason, even if there is room in the electric double layer capacitor, there is a problem that the life cannot be extended.

  An object of the present invention is to provide a method for compensating a DC standby voltage of an electric double layer capacitor that can extend the life.

Claim 1 of the present invention is an instantaneous voltage drop compensator that connects an AC / DC converter to an electric power system and supplies electric power to a load via the AC / DC converter using an electric double layer capacitor as a power source when the voltage of the electric power system drops. In order to set the DC voltage during the low voltage standby of the electric double layer capacitor and the recharge start voltage,
Capacitance and internal resistance after a predetermined period are obtained from the secular change of the electric double layer capacitor, and the electrostatic capacity and internal resistance are substituted into a discharge time calculation formula to obtain a capacitor voltage during standby for a short time. It is what.

  According to a second aspect of the present invention, the capacitance and the internal resistance of the electric double layer capacitor are determined every predetermined time, and the voltage of the capacitor that is waiting for a sag during the predetermined time using the calculated capacitance and internal resistance is determined. It is characterized by changing.

  According to a third aspect of the present invention, the electrostatic capacitance and the internal resistance of the electric double layer capacitor detect the charging current and the capacitor voltage after the instantaneous drop compensation of the instantaneous drop voltage compensator, and the internal resistance R determines the capacitor. R = ΔV / I (where I is the capacitor charging current before constant power charging) from the DC voltage drop ΔV when the current is zero from the power charging state, and the capacitance is determined from the charging curve of the capacitor voltage. It is characterized by that.

  According to a fourth aspect of the present invention, the capacitance and internal resistance of the electric double layer capacitor are obtained by performing a characteristic diagnosis of the capacitor every predetermined time, and performing a constant power charge after discharging the capacitor at a constant power. It is what.

Claim 5 of the present invention is an instantaneous voltage drop compensator that connects an AC / DC converter to a power system and supplies power to a load via the AC / DC converter using an electric double layer capacitor as a power source when the voltage of the power system drops. In order to set the DC voltage during the low voltage standby of the electric double layer capacitor and the recharge start voltage,
The detected power system voltage and load current are dq converted to obtain active power, and the calculated active power is substituted into a discharge time calculation formula to obtain a capacitor voltage during standby for a sag. Is.

  A sixth aspect of the present invention is characterized in that the capacitor voltage during the low voltage standby calculated by any one of the first to fifth aspects is applied to a control system for stopping the AC / DC converter in normal times. is there.

  As described above, according to the present invention, it is possible to extend the life of a capacitor by setting the capacitor voltage during standby for a short time to a rated value or less. In addition, the number of capacitors used in the device can be reduced due to the slow deterioration over time.

Prior to the description of the embodiments of the present invention, the basic idea will be described.
FIG. 6 shows a configuration diagram of the electric double layer capacitor 1, and n electric double layer capacitor units 10 are connected in series and m arms connected in series are connected in parallel. The discharge time of the electric double layer capacitor 1 configured in this way can be calculated as follows. Table 1 shows parameters used for the calculation.

The energy E stored in the electric double layer capacitor can be calculated by E = 1/2 · CV ^{2 from} the DC voltage V of the capacitor. In the calculation of the discharge time in units of electric double layer capacitor units, first, the output power is obtained based on equation (1). From total load power, number of units, and conversion efficiency

It becomes.
It is assumed that the battery is charged up to the maximum voltage Vmax at the start of discharge. As shown in FIG. 7, the terminal voltage drops from the maximum voltage due to the voltage drop due to the discharge current I and the internal resistance as the discharge starts. The terminal voltage Vs at this time is expressed by equation (2).

Further, the relationship between the terminal voltage V during discharge and the internal resistance V0 is expressed by equation (3).

Moreover, since the energy stored in the capacitor is reduced by the discharge, the equation (4) is obtained. Here, A is an integral constant. When t = 0, since V = Vs, the equation (5) is obtained.

Therefore, the discharge time tmax when V = Vmin is given by equation (6).

Here, when arranging using Vr = Vmin / Vmax, equation (7) is obtained.

Therefore, the discharge time tmax can be calculated by equation (7).
The discharge time tmax is a value of the capacitance and internal resistance after the device lifetime has elapsed, and is set to be equal to or greater than the specification of the instantaneously low operating time. Thereby, it is possible to satisfy the use of the instantaneously low operating time without raising the capacitor voltage to the rated value in the initial state.

  As an example, if the capacitance of the capacitor is designed under the condition that the capacitance after 15 years is -24% and the internal resistance is + 24% in the specification of Table 2, the result shown in Table 3 is obtained. In the design example, 280 cells are connected in series.

Generally, it is said that when the applied voltage per cell of an electric double layer capacitor is lowered by 0.3 V, the deterioration rate of the capacitor is halved.
According to the design result of the capacitor according to the present invention, as shown in Table 3, the capacitor was designed to compensate for an instantaneous drop of 2.5 (s) after 15 years, and initially compensated for 4.3 (s). Even if the capacitor voltage is not increased to 640 V, which is rated V1, 2.5 (s) sag compensation can be achieved. In the present invention, the equation (7) is solved for Vmax, and the capacitor voltage during the low voltage standby is determined using the equation. The voltage drop compensation time is substituted for the discharge time tmax.

  FIG. 1 is a transition diagram of capacitor voltage setting values according to an embodiment of the present invention. This embodiment is applied to the floating charging method in which the AC / DC converter is operated at all times. The capacitor voltage setting value after a certain period is calculated in advance, and the capacitor voltage setting value calculated after the lapse of the period is read. It is. In order to determine the capacitor voltage during the low voltage standby, the unit capacitance C and the unit internal resistance R are obtained by the equation (8).

The aging of the capacitor changes in proportion to √ (time). Equation (8) assumes that the characteristics change to -24% after 15 years and the internal resistance to + 24% (at an ambient temperature of 25 ° C.) due to aging of the capacitor, as in the example described above. C and R are obtained. C and R are obtained from the equation (8), and the instantaneous drop compensation time is used as the discharge time tmax. By substituting C, R, and tmax into the equation (7), the capacitor voltage Vmax during standby for a sag is determined. As the values of C and R, for example, values obtained every one month are obtained, and the capacitor voltage during standby for a sag is changed as shown in FIG. Here, V1 is a rated voltage of the apparatus, and V2 is a charging start setting voltage value.

  According to this embodiment, the capacitor voltage setting value after a certain period is obtained from C and R obtained by the prediction formula of the secular change of the capacitor, and the capacitor voltage in the low voltage standby state is changed every time the period elapses. Therefore, it can be easily implemented.

The deterioration characteristics of the electric double layer capacitor vary depending on the ambient temperature and the number of sag compensation operations. Therefore, the second embodiment corrects the calculation value of the first embodiment.
After performing the sag compensation operation, the sag compensation device performs charging to prepare for the next sag compensation operation. In this embodiment, the capacitance / internal resistance is corrected each time the voltage sag compensation operation is performed using the charging current and capacitor voltage at that time, and the deterioration characteristics of the capacitor are corrected.

If the charging current is reduced to zero from the state where the capacitor is charged at a constant power, the DC voltage decreases due to the internal resistance of the capacitor. From the decrease ΔV, the internal resistance R can be obtained by R = ΔV / I. (Where I is the capacitor charging current immediately before constant voltage charging.)
C can be obtained from the charging curve of the capacitor voltage.

By substituting the calculated C and R into the equation (7) in the same manner as in the first embodiment, it is possible to determine the capacitor voltage Vmax during the standby for instantaneous drop.

  Note that the instantaneous drop compensation operation is not always performed periodically. If the instantaneous drop compensation operation is not executed for a long period of time, there is a concern that an error from the actual value becomes large. In such a case, C and R may be obtained by conducting a characteristic diagnosis of the capacitor periodically and performing constant power charging after discharging the capacitor with constant power.

  According to this embodiment, the DC voltage / charging current at the time of recovery charging after the sag compensation operation and the equation (9) or periodically aging diagnosis of the capacitor is performed, and the DC voltage / charging current at the time of diagnosis is determined. Since the set voltage is obtained from the capacitance obtained from the equation (9) and the internal resistance, the capacitor voltage set value can be obtained more accurately than in the first embodiment.

In Examples 1 and 2, the discharge power of the capacitor is considered to be constant (rated). In practice, the load power is often smaller than the rating. In the third embodiment, the load power is monitored and the discharge power P of the capacitor is changed.
Since the capacitor outputs active power, in order to obtain the discharge power P, the effective power of the load may be obtained. The effective power can be obtained from the system voltage / load current obtained by the dq conversion by the equations (10), (11), and (12).

By using the above equation for P in equation (7), the capacitor voltage can be obtained.

  According to this embodiment, since the effective power of the load is obtained and the set voltage of the capacitor is changed in accordance with the effective power of the load, the capacitor voltage can be lowered when the load is light. As compared with, the deterioration rate of the capacitor can be further suppressed.

  Each of the above embodiments is applied to a floating charging system in which the AC / DC converter is always operated. However, the fourth embodiment is applied to a system in which the AC / DC converter is normally stopped. FIG. 2 is a state diagram of capacitor voltage setting based on this embodiment, where V1 is a rated voltage of the capacitor, V2 is a charge start set voltage value, V3 is a corrected charge start set voltage value, It is a capacitor voltage setting value corrected for deterioration characteristics calculated based on the embodiment.

When the rated voltage V1 is reached at time t1 from the start of charging of the capacitor 1, the charging operation by the AC / DC converter 4 is stopped. When the voltage of the capacitor 1 gradually decreases from the time t1 and decreases to the charging start set voltage value V2 at the time t2, the AC / DC converter 4 operates in the charging mode and starts charging, and reaches the rated voltage at the time t3. The AC / DC converter 4 stops again.
On the other hand, the control circuit of the AC / DC converter 4 obtains the capacitance C and the internal resistance R of the capacitor after a certain period (after time t2 in FIG. 2), and substitutes the obtained CR into the equation (7). Determine the voltage. This calculated voltage is set as V3, and becomes the charge start setting voltage value at time t4. Thereafter, the AC / DC converter 4 is repeatedly stopped and operated in the same manner.

  According to this embodiment, it is possible to suppress the deterioration rate of the capacitor as in each of the above embodiments, and it is possible to reduce the apparatus loss during standby because the AC / DC converter stop period becomes longer. .

The transition figure of the capacitor voltage setting value which shows the embodiment of the present invention. The transition figure of the capacitor voltage setting value which shows other embodiment of this invention. The block diagram of an instantaneous voltage drop compensation apparatus. Explanatory drawing of the charge system which stops an AC / DC converter. Explanatory drawing of the floating charge system of an AC / DC converter. FIG. The time change figure of the capacitor voltage and electric current by discharge.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric double layer capacitor 2 ... Load 3 ... High speed switch 4 ... AC / DC converter 5 ... System power supply 10 ... Electric double layer capacitor unit

Claims (6)

An instantaneous voltage drop compensator that connects an AC / DC converter to an electric power system and supplies power to a load via the AC / DC converter using the electric double layer capacitor as a power source when the voltage of the electric power system drops. For setting the DC voltage and recharge start voltage during standby for low voltage,
Capacitance and internal resistance after a predetermined period are obtained from the secular change of the electric double layer capacitor, and the electrostatic capacity and internal resistance are substituted into a discharge time calculation formula to obtain a capacitor voltage during standby for a short time. DC standby voltage compensation method for instantaneous voltage drop compensator. Capacitance and internal resistance of the electric double layer capacitor are determined every predetermined time, and the capacitor voltage during the instantaneous drop standby is changed every predetermined time using the obtained capacitance and internal resistance. A method of compensating for a DC standby voltage of an instantaneous voltage drop compensator according to claim 1. The electric capacitance and internal resistance of the electric double layer capacitor detect the charging current and capacitor voltage after compensation for the instantaneous drop operation of the instantaneous voltage drop compensator, and the internal resistance R sets the capacitor to zero current from the constant power charging state. 2. The DC voltage drop at the time ΔV is obtained by R = ΔV / I (where I is a capacitor charging current before constant power charging), and the capacitance is obtained from a charging curve of the capacitor voltage. Or the DC standby voltage compensation method for the instantaneous voltage drop compensator according to 2 above. The instantaneous capacitance according to claim 3, wherein the capacitance and the internal resistance of the electric double layer capacitor are obtained by performing a characteristic diagnosis of the capacitor every predetermined time and performing a constant power charge after discharging the capacitor at a constant power. DC standby voltage compensation method for drop voltage compensator. An instantaneous voltage drop compensator that connects an AC / DC converter to an electric power system and supplies power to a load via the AC / DC converter using the electric double layer capacitor as a power source when the voltage of the electric power system drops. For setting the DC voltage and recharge start voltage during standby for low voltage,
The detected power system voltage and load current are dq converted to obtain active power, and the calculated active power is substituted into a discharge time calculation formula to obtain a capacitor voltage during a sag standby. DC standby voltage compensation method for instantaneous voltage drop compensator.
6. The instantaneously low standby capacitor voltage calculated according to any one of claims 1 to 5 is applied to a control method for stopping the AC / DC converter in normal times. DC standby voltage compensation method for drop voltage compensator.

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